AFAIK the most important difference between WASM and other VMs on the level of CLR or JVM is that WASM has a simple linear memory model, which allows languages which expect a linear heap (like C, C++, Rust, ...) to be supported by just adding new backends to existing compilers (and most importantly without requiring changes to the language).

The CLR and JVM might be able to simulate a linear heap through a byte array (just like asm.js did), but it's questionable whether this allows the same performance as WASM when the whole VM instruction set is built around high level object references.

CLR doesn't need to simulate anything, its bytecode is expressive enough for languages like C and C++.